Micro-Injection Pump

ABSTRACT

A micro-injection pump for angiography and micro-intervention procedures comprises first and second linear traverses each have a pusher element movable by stepper motor drive for controlling discharge from a respective micro-syringe engaged by the pusher element. The first micro-syringe preferably contains a volume of a soluble contrast medium, and the second micro-syringe preferably contains a volume of an insoluble contrast medium. Fluid discharged by the micro-syringes is directed to a bifurcated micro-droplet generator having a straight primary passage and an obliquely merging tributary passage. Insoluble contrast medium from the second micro-syringe flows through a micro-sized injection needle extending partially and coaxially within the primary passage to a termination point just downstream from where the tributary passage joins the primary passage. Soluble contrast medium from the first micro-syringe passes through the tributary passage to provide a flow field surrounding the injection needle for shearing off discrete same-sized boluses from the terminal tip of the injection needle at regular frequency in coordination with a predetermined motion profile of the first and second linear traverses. Motion control of the linear traverses is possible using LABVIEW® virtual instrumentation software arranged to communicate with a 2-axis indexer control connected to first and second motor indexers for driving the stepper motors of the linear traverses. Linear potentiometers on the linear traverses, rotary encoders connected to the motors, a flowmeter, and pressure transducers indicate motion and flow parameters of the system in real-time to provide a feedback loop in the system so that a desired media delivery waveform is realized.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent application Ser. No. 60/213,319 filed Jun. 22, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to the field of controlled injection devices used to inject contrast media for angiography and therapeutic fluids for micro-intervention, and more particularly to a high-pressure micro-injection pump capable of injecting precise micro-liter fluid volumes into the vasculature and accurately controlling the velocity, acceleration, and timing of the injected fluid volumes. The present invention finds particular application in the field of high-speed pulsed digital subtraction angiography (DSA).

[0004] 2. Description of the Related Art

[0005] Devices for controlled injection of radiopaque dye into the bloodstream through micro-catheters are known from the art of angiography for evaluation of blood flow patterns. U.S. Pat. No. 3,623,474 describes an angiographic injector system having automatic syringe drive means controlled by a programmable command signal, such that an operator may select an injection flow rate. The actual flow rate is monitored and a feedback signal is generated to maintain the desired flow rate regardless of flow attenuating factors such as catheter internal diameter, catheter length, contrast medium viscosity, and flow path configuration. The described system includes a rate trip circuit for preventing delivery of excessive flow to the patient should the control system fail. An improved angiographic control system by the same inventors is disclosed in U.S. Pat. No. 3,701,345, wherein syringe position follows a position command signal with the guidance of a syringe position feedback signal. U.S. Pat. No. 3,812,843 teaches an apparatus for injecting contrast media either sequentially at two different rates or at one rate, depending upon flow requirements. Where two different rates are selected, the duration of each can be specified.

BRIEF SUMMARY OF THE INVENTION

[0006] It is therefore an object of the present invention to provide a micro-injection pump capable of delivering precise micro-liter fluid volumes into the vasculature and accurately controlling the velocity, acceleration, and frequency of the injected fluid volumes.

[0007] It is another object to provide a micro-injection pump with a graphic motion control interface that is simple to use.

[0008] It is a further object of the present invention to provide a micro-injection pump with motion and flow sensing devices for providing real-time feedback to the motion control system to correct delivery parameters to follow a desired waveform.

[0009] It is a further object of the present invention to provide a micro-injection pump that is compatible with a variety of syringes and micro-catheters commonly in use.

[0010] A micro-injection pump formed in accordance with a preferred embodiment of the present invention generally comprises first and second linear traverses each having a syringe holder for holding respective first and second micro-syringes, and a carriage-mounted pusher element for engaging a plunger of the associated micro-syringe. The first micro-syringe preferably contains a volume of a soluble contrast medium, and the second micro-syringe preferably contains a volume of an insoluble contrast medium. Each linear traverse includes a stepper motor for allowing very accurate control of the position, velocity, and acceleration of the traverse carriage.

[0011] Fluid discharged by the micro-syringes is directed to a bifurcated micro-droplet generator having a straight primary passage and an obliquely merging tributary passage. More specifically, insoluble contrast medium from the second micro-syringe flows through a micro-sized injection needle extending partially and coaxially within the primary passage to a termination point just downstream from where the tributary passage joins the primary passage. Soluble contrast medium from the first micro-syringe is routed through the tributary passage to provide a flow field surrounding the injection needle, thereby providing shear force to separate discrete same-sized boluses from the terminal tip of the injection needle at regular time intervals in coordination with a predetermined motion profile of the first and second linear traverses.

[0012] Motion control of the linear traverses is possible using LABVIEW® virtual instrumentation software arranged to communicate with a 2-axis indexer control connected to first and second motor indexers for driving the stepper motors. Linear potentiometers mounted on the traverses, rotary encoders connected to the stepper motors, a flowmeter, and pressure transducers indicate motion and flow parameters of the system in real-time to provide a feedback loop in the system so that a desired media delivery waveform is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the preferred embodiments taken with the accompanying drawing figures, in which:

[0014]FIG. 1 is a perspective view of a micro-injection pump formed in accordance with a preferred embodiment of the present invention;

[0015]FIG. 2 is a top plan view of the micro-injection pump shown in FIG. 1, with syringe plungers in a ready position;

[0016]FIG. 3 is a partial top plan view similar to that of FIG. 2, with syringe plungers in a discharged position;

[0017]FIG. 4 is a partially sectioned detail view taken generally along the line 4-4 in FIG. 1 showing a micro-droplet generator of the present invention; _

[0018]FIG. 5 is a schematic view illustrating initial formation of a liquid bolus of insoluble contrast medium by the micro-droplet generator shown in FIG. 4;

[0019]FIG. 6 is a schematic view similar to that of FIG. 5 illustrating separation and conveyance of a liquid bolus of insoluble contrast medium;

[0020]FIG. 7 is a schematic system diagram showing currently preferred hardware connections of the present invention;

[0021]FIG. 8 is a screen capture of a LABVIEW® front panel showing a Contrast Injector virtual instrument (VI) for operating the micro-injection pump of the present invention;

[0022]FIG. 9 shows a first of three main LABVIEW® graphical object-based software sequence frames associated with the Contrast Injector VI, wherein the first frame comprises an initializing and homing configuration routine for the Contrast Injector VI;

[0023]FIG. 10A shows a second of three main LABVIEW® software sequence frames associated with the Contrast Injector VI, wherein the second frame comprises a main sequence structure associated with the Contrast Injector VI depicted with blank schematic representations of independent sequences (2) through (6) illustrated fully in subsequent figures;

[0024]FIG. 10B fully shows LABVIEW® software sequences (2) and (3) represented schematically in FIG. 10A;

[0025]FIG. 10C fully shows LABVIEW® software sequence (4) represented schematically in FIG. 10A;

[0026]FIG. 10D fully shows LABVIEW® software sequences (5) and (6) represented schematically in FIG. 10A;

[0027]FIG. 11 shows a third of three main LABVIEW® software sequence frames associated with the Contrast Injector VI, wherein the third frame comprises a shut down routine for the Contrast Injector VI;

[0028]FIG. 12 is a screen capture of a LABVIEW® front panel showing a Profile Tracker virtual instrument (VI) for operating the micro-injection pump of the present invention according to a predefined injection flow profile chosen by the user;

[0029]FIG. 13 shows a first of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, wherein the first frame comprises an initializing and homing configuration routine for the Profile Tracker VI;

[0030]FIG. 14A shows a second of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, including a Trace Option alternative case control structure shown in its true condition, a second of three sequence sub-frames nested in the Trace Option alternative case control structure, and an inner alternative case control structure nested in the second sequence sub-frame shown in its true condition;

[0031]FIG. 14B shows the Trace Option alternative case control structure shown in FIG. 14A, however in its false condition;

[0032]FIG. 14C shows a first of three sequence sub-frames nested in the Trace Option alternative case control structure shown in FIG. 14A;

[0033]FIG. 14D shows a third of three sequence sub-frames nested in the Trace Option alternative case control structure shown in FIG. 14A;

[0034]FIG. 14E shows the inner alternative case control structure nested in the second sub-frame sequence shown in FIG. 14A, however in its false condition; and

[0035]FIG. 15 shows a third of three main LABVIEW® software sequence frames associated with the Profile Tracker VI, wherein the third frame comprises a shut down routine for the Profile Tracker VI.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Referring initially to FIGS. 1-3, a micro-injection pump 10 of the present invention is shown as comprising a first linear traverse 12 operable along a first axis 12A, and a second linear traverse 14 operable along a second axis 14A. First linear traverse 12 includes a track 12B and a carriage 12C mounted on track 12B for back and forth driven motion along first axis 12A. A stepper motor 12D is located at a front end of first linear traverse 12 and connected to carriage 12C via a drive coupler 12E and drive shaft (not shown). Carriage 12C supports an upstanding pusher element 12F which is axially movable with the carriage relative to a stationary syringe holder 12G provided near the front of first linear traverse 12. Travel limit switches 12H are also provided. Likewise, second linear traverse 14 includes a track 14B, carriage 14C, stepper motor 14D, drive coupler 14E, pusher element 14F, syringe holder 14G, and limit switches 14H in similar arrangement.

[0037] As can be seen, syringe holder 12G on first linear traverse 12 holds a first micro-syringe 16 preferably filled with an amount of a soluble contrast medium 18. First micro-syringe 16 includes an axially movable plunger 16A having a distal end 16B engaged by pusher element 12F. Syringe holder 14G on second linear traverse 14 holds a second micro-syringe 20 which, for evaluation and intervention applications, may be filled with an amount of an insoluble contrast medium 22 such as ETHIODOL® available from Savage Laboratories of Melville, N.Y. Second micro-syringe 20 includes an axially movable plunger 20A having a distal end 20B engaged by pusher element 14F. First and second micro-syringes 16 and 20 are in flow communication with a micro-droplet generator 28 by way of catheter tubes 24 and 26 respectively coupled to the outlet ports of micro-syringes 16 and 20. Micro-droplet generator 28 feeds a micro-catheter 29 in flow communication with the vasculature of a patient.

[0038] Micro-droplet generator 28 is shown in detail in FIGS. 4-6. Micro-droplet generator 28 includes a bifurcated junction member 30 upstream from a reducer 32 threadably joined thereto. Junction member 30 includes a tributary port 30A fed by first micro-syringe 16 via catheter tube 24 and closable valve 25, an inlet port 30B fed by second micro-syringe 20 via catheter tube 26, and an outlet port 30C opposite inlet port 30B. Inlet port 30B is connected for flow communication with outlet port 30C by a straight primary passageway 30D, and tributary port 30A is connected for flow communication with primary passageway 30D by a tributary passageway 30E forming an acute angle with primary passageway 30D. A narrow injection needle 34 extends partially within primary passageway 30D from inlet port 30B to a region just downstream from the junction of tributary passageway 30E with primary passageway 30D. Clearance is provided between the outer wall of injection needle 34 and the inner wall defining primary passageway 30D to allow fluid to occupy the intervening space. For example, in the preferred embodiment primary passageway 30D has an inner diameter of 2.00 mm. An adjustable sealing coupler 36 normally provides a fluid tight seal about injection needle 34, and can be loosened to bleed the system such that fluid that is free of air bubbles occupies the intervening space. Based on the above arrangement of micro-161 droplet generator 28, it is apparent from FIGS. 5 and 6 that flow of soluble contrast medium 18 within primary passageway 30D about injection needle 34 exerts a shear force upon boluses 22A of insoluble contrast medium 22 forming at the tip of the injection needle, thereby separating and conveying each bolus for travel through a reducer 32 connectable to a micro-catheter 29 by a leur lock 31. By controlling the motion of linear traverses 12 and 14, a series of same-sized boluses 22A having identifiable velocity and acceleration characteristics can be released at a desired regular frequency.

[0039] In accordance with the present invention, micro-liter precision for injection volumes and accurate control of dosage velocity and acceleration are achieved by computerized motion control of first and second linear traverses 12 and 14 actuating micro-syringes 16 and 20, respectively. Linear traverses 12 and 14 can be controlled according to any predetermined profile to achieve necessary delivery parameters. The schematic system diagram of FIG. 7 illustrates the currently preferred hardware arrangement for micro-injection pump 10. Stepper motor 12D is connected to a first motor indexer drive 46 by lead 48, and stepper motor 14D is connected to a second motor indexer drive 50 by lead 52. First and second indexer drives 46 and 50 are, for example, Parker Compumotor Zeta 4 drives having respective motor drive ports 54 and 56 to which leads 48 and 52 are connected. A 2-axis indexer control 58 is linked for serial communications with a central processing unit 60 via an RS232 cable 62. In keeping with the present example embodiment, indexer control 58 is a Parker Compumotor 6200 controller with dual axis capability, and RS232 cable 62 is linked to an auxiliary port 64 of indexer control 58. The indexer control board includes a Drive 1 port 66 connected by cable 68 to an indexer port 70 on first motor indexer drive 46, and a Drive 2 port 72 connected by cable 74 to an indexer port 76 on second motor indexer drive 50. Indexer control 58 further includes a limit switch port 78 to which limit switches 12H and 14H can be connected by leads 80 and 82.

[0040] Hardware is preferably installed for providing feedback information to computer 60 describing system variables. A pair of linear potentiometers 84 and 86 are matched with first and second linear traverses 12 and 14, respectively, for tracking position, velocity, and acceleration information with regard to each traverse in real time. A suitable linear potentiometer for the example system described herein is a Type HLP190/SA1/150/6K available from Penny & Giles Controls Limited. In addition to linear potentiometer feedback, two rotary encoders 85 and 87 are also employed for position, velocity, and acceleration feedback with respect to first and second linear traverses 12 and 14. Encoders 85 and 87 are attached to corresponding drive motors 12D and 14D via a flexible shaft connection. A suitable encoder for the example system described herein is a model C150/152/153 distributed by Dynamic Research Corp, having a resolution of 8000 counts per revolution. A pair of pressure transducers 88 and 90, available for example from Validyne of Northridge, Calif., monitor fluid pressure as fluid exits first and second micro-syringes 16 and 20, respectively. In addition, a flowmeter 92 is preferably installed to measure flow rates for each micro-syringe. The model T206 flowmeter available from Transonic Systems Inc. of Ithaca, N.Y. can perform this function.

[0041] User interface and control of the micro-injection pump of the present invention is currently configured using LABVIEW® virtual instrumentation software available from National Instruments Corporation. FIG. 8 is a screen capture of a Contrast VI front panel 100 showing a virtual control screen for operating micro-injection pump 10. Contrast Injection front panel 100 includes a home button 102 for running a home positioning routine, a start button 104, a stop button 106, and an escape button 108. A quit button 110 is also provided for exiting from front panel 100. A two-axis graphical display 112 reports theoretical and measured flow rates in real time for first and second micro-syringes 16 and 20, with corresponding digital readouts 114 and 116 preferably being provided as well. Stepper motors 12D and 14D can be assigned “soft” travel limits in the clockwise and counter-clockwise directions using digital controls 118A, 118B and 118C, 118D, or using their corresponding pointers 119A, 119B and 119C, 119D on bar graphs 121 and 123, respectively. Bar graphs 121 and 123 provide a visual indication of the individual syringe volumes injected by first micro-syringe 16 and second micro-syringe 20, measured in cubic centimeters, with the scale of each bar graph being dependent upon the chosen syringe size. Corresponding digital displays 122 and 124 also report the injected volumes for the respective syringes in digital format. In addition, two pairs of LED indicators 120A, 120B and 120C, 120D illuminate when the traverse has crossed the associated soft limit setting.

[0042] Controls for first linear traverse 12 include a syringe size selector 126 and a velocity knob control 128. A digital flow rate control terminal 130 shows the flow rate in cc/sec based on the selected syringe size and velocity, and can be used to directly choose a desired flow rate and thus set a corresponding velocity. Likewise, controls associated with second linear traverse 14 include a syringe size selector 132, a velocity knob control 134, and a digital flow rate control terminal 136. A predetermined time delay for starting motion of second linear traverse 14, if desired, is selectable at delay control portion 138 of front panel 100. A hardware trigger button 139 (Digital Trigger Enable) is also provided to enable synchronized injections with ECG and angiographic equipment. Below hardware trigger button 139 is a profile tracker button 140 (Profile Tracker Enable) which is used to call the Profile Tracker VI software. Upon depression of this button, execution of the Contrast Injector VI software is suspended while the Profile Tracker VI software is loaded and run. A Profile Tracker front panel, described below, stays in the foreground until the user exits from the Profile Tracker front panel, at which time the Contrast Injector front panel 100 will come to the foreground and re-engage. Finally, a linear traverse direction toggle 141 and a soft limit enable toggle 142 allow further control of microinjection pump 10.

[0043] FIGS. 9, 10A-10D, and 11 are directed to three main sequence frames of the Contrast Injector VI. FIG. 9 shows a first frame 144 containing a motor controller initializing routine and a homing configuration routine. Home configuration blocks 146 and 148 determine the velocity, acceleration, and deceleration of the homing routines for first linear traverse 12 and second linear traverse 14, respectively. Additionally, there is a parameter precision “sub-VI” 145 which is preferably used to specify a three decimal place level of precision on all numbers sent to the motor controller 58, thereby improving communications performance. Motion scaling sub-VIs 147 and 149 are issued to scale position, velocity, and acceleration parameters for the specified motors.

[0044] FIGS. 10A-10D show a second frame 150 containing a main sequence structure of the Contrast Injector VI software. A main “while loop” 152 contains six independent sequence frames (1)-(6), an alternative case structure (7), and sub-VIs 151 for stopping the program and halting motor motion. Sequence (1) takes in velocity information from the velocity knob controls 128 and 134, scales the data and sends the information to the motor controller. Sequence (1) also provides a direction sub-VI 153 for setting the travel direction of both linear traverses. Sequence (2), best seen in FIG. 10B, acquires, scales, and plots position and velocity (volume and flow rate) ascertained by linear potentiometers 84 and 86 affixed to the linear traverses 12 and 14. Sequence (3), also shown in Fig. 10B, is used to scale slider bars 121 and 123, which indicate volumes injected for each syringe pump, and also to scale the appropriate soft limit controls. Sequence (4) shown in Fig. 10C enables and disables both the delay timer and the hardware trigger. Within this sequence are two nested alternative case structures 154 and 156. The outer most case structure 154 enables or disables the hardware trigger by checking the hardware trigger button 139 on the front panel. If the hardware trigger is engaged, the system can be started by clicking on the start button 108 or by reading a transistor transistor logic (TTL) digital input high, acquired from controller 58. This is especially useful when injections need to be synchronized with an angiographic run or with the cardiac cycle. The inner case structure 156 enables or disables the second linear traverse delay timer. Referring now to FIG. 10D, sequence (5) is used to scale and set “soft” limits. Sequence (6) checks the software limits'status and sends pass/fail information to LED indicators 120A-120D on Contrast Injector front panel 100. The final structure in while loop 152 (FIG. 10A) is an alternative case structure (7) used to call a secondary program, namely the Profile Tracker VI mentioned above.

[0045]FIG. 11 shows a third frame 160 of the Contrast Injector VI for shutting down the apparatus. Inputs to an enable motor drive sub-VI 162 are changed to disable the motor drives, and a close device sub-VI 164 is executed for shutting down the virtual instrumentation.

[0046]FIG. 12 shows a front panel 200 of the Profile Tracker VI software mentioned above. The Profile Tracker program is utilized during injection of embolic agents, and has the capability of injecting a single syringe of fluid at a variable rate. The user predetermines the rates of injection by selecting a predefined injection flow profile from a Profile Menu presented by a drop down text box 201. The user can also run new and unique profiles with the system by selecting “user defined profile” in the aforementioned drop down menu. The user needs only to create a profile data set in “.txt” format and in units of cc/sec, and load the data set into the program. Similar to the Contrast Injector VI front panel 100, the Profile Tracker VI front panel 200 has motion control buttons including a home button 202, a start button 204, a stop button 206, and a quit button 210. A syringe size/loading control panel 212 includes a drop down menu 214 from which a user can select one of a plurality of standard and user-programmable syringe sizes, and a load toggle 216 for moving carriage 14C and pusher element 14F into proper position for loading and unloading syringes.

[0047] The Profile Tracker VI includes a proportional plus integral plus derivative (P.I.D.) feedback control loop to ensure proper tracking of specified injection flow profiles. The P.I.D. VI controls are placed in a “PID Parameter Settings & Gain Scheduling” panel 220. These controls allow the user to tune the P.I.D. controller. The graph 228 plots the predetermined profile data in solid white line and the Profile Trackers VI's real time actual flow profile data in colored circles. There are four basic steps to using the Profile Tracker VI: first, load a desired syringe; second, select the corresponding syringe size; third, choose a preferred injection flow profile from profile menu 201; and fourth, select “Start Profile Tracker” button 203 when ready.

[0048] Reference is now made to FIG. 13, which illustrates a first frame 230 of three main sequence frames of the Profile Tracker VI. First frame 230 includes a motor controller initializing routine and homing configuration routine. Home configuration sub-VIs 232 and 234 determine the velocity, acceleration and deceleration of the homing routines for first linear traverse 12 and second linear traverse 14, respectively.

[0049] FIGS. 14A-14E show a second frame 240 containing a main sequence structure of the Profile Tracker VI. Within second sequence frame 240 is a main while loop 242 used to run the program until the quit button 210 on front panel 200 has been depressed (see lower right corner of FIG. 14A). The while loop 242 contains a file selector sub-VI 244 which is used to retrieve a predetermined injection profile or allows the user to search for a specific file. Data and trace graph attribute nodes 246 and 248 respectively ensure that the data graph and the real time trace graph have the same scaling. There is also a linear potentiometer sub-VI 250 and a velocity scaler sub-VI 252 in the main while loop 242. A motor engage control sub-VI 254 has an alternate case structure 256 adjacent to it in order to enable resetting or unlatching of the start button 204 after it has been depressed.

[0050] Attention is now directed to alternate case structure 260, sequence sub-frame 262, alternate case structure 264, and while loop 266 located in nested arrangement at the right side of second frame 240. The outer most alternate case structure 260 is a Trace Option case structure used to determine if the profile trace program should be initiated, as determined by the Start Profile Tracker button 203 located on the front panel 200. If button 203 is “ON”, Trace Option case structure 260 executes according to the “true” condition as depicted in FIG. 14A. If button 203 is “OFF”, Trace Option case structure 260 executes according to the “false” condition as depicted in FIG. 14B. The execution of inner alternate case structure 264 is likewise determined by Start Profile Tracker button 203, with a “false” condition of case structure 264 being shown in FIG. 14E. The nested sequence sub-frame 262, which is the second in a series of three sub-frames 261-263, serves to dump the data from a selected injection profile file to the P.I.D. control loop and to designate a time base for the data to be read and moves to be executed. FIG. 14C shows first sequence sub-frame 261 which functions to clear the feedback history data of the trace graph 228. FIG. 14D shows third sequence sub-frame 263 programmed to ask the user if he or she would like to run another profile by bringing up a pop up window with yes and no buttons. This function is disengaged when the user clicks quit button 210. Third sub-frame 263 also unlatches both Start Profile Tracker button 203 and stop button 206.

[0051] A third frame 270 of the three main sequence frames of the Profile Tracker VI is shown in FIG. 15, and is similar to the third frame 160 of Contrast Injector VI 160. Third frame 270 shuts down the apparatus by changing inputs to an enable motor drive sub-VI 272 to disable the motor drives and by executing a close device sub-VI 274 for closing down the virtual instrumentation.

[0052] As will be appreciated from the above description, the micro-injection pump of the present invention maintains accurate flow rates under high pressure loading. In preliminary testing, a micro-injection pump as described above demonstrated the capability to deliver 1.0±0.1 microliters at high pressure up to 20 atmospheres. Micro-injection pump 10 is compatible with a an assortment of syringes and micro-catheters commonly used in micro-intervention procedures. While not described above, it is of course advisable to provide safety features, such as automatic shut-off and alarm features, to prevent serious complications in the event of a system malfunction.

[0053] Benefits of the present invention include improved quantitative measurements of blood flow patterns, more precise transit time estimates, and greatly improved visualization of complex hemodynamics associated with arteriovenous malformations. 

What is claimed is:
 1. A micro-injection pump comprising: a bifurcated micro-droplet generator including a tributary passage merging with a primary passage, and an injection needle extending within said primary passage to a termination point downstream of a location where said tributary passage merges with said primary passage; a first syringe in fluid communication with said tributary passage for supplying a first fluid, said first syringe having a plunger; a second syringe in fluid communication with said injection needle for supplying a second fluid, said second syringe having a plunger; a first linear traverse operatively connected to said plunger of said first syringe for controllably discharging said first fluid from said first syringe; a second linear traverse operatively connected to said plunger of said second syringe for controllably discharging said second fluid from said second syringe; and a catheter arranged downstream of said micro-droplet generator; whereby said first fluid is used to separate droplets of said second fluid from said injection needle at said termination point and carry said droplets through said catheter.
 2. The micro-injection pump according to claim 1, further comprising computer control means connected to said first and second linear traverses for controlling the respective motions of said first and second linear traverses.
 3. The micro-injection pump according to claim 2, further comprising at least one sensor associated with said first linear traverse and connected to said computer control means for measuring position, velocity, and acceleration of said first linear traverse, and at least one sensor associated with said second linear traverse and connected to said computer control means for measuring position, velocity, and acceleration of said second linear traverse.
 4. The micro-injection pump according to claim 3, wherein said at least one sensor associated with said first linear traverse and said at least one sensor associated with said second linear traverse include a linear potentiometer.
 5. The micro-injection pump according to claim 3, wherein said at least one sensor associated with said first linear traverse and said at least one sensor associated with said second linear traverse include a rotary encoder.
 6. The micro-injection pump according to claim 2, further comprising a pair of pressure sensors associated one with each of said first and second syringes and connected to said computer control means for measuring fluid pressure in said first and second syringes, respectively.
 7. The micro-injection pump according to claim 2, further comprising a pair of flowmeters associated one with each of said first and second syringes and connected to said computer control means for measuring flow rate of said first and second fluids, respectively.
 8. The micro-injection pump according to claim 2, wherein said computer control means includes a user interface having a delay control portion for assigning a user-selectable time delay for delaying the start of the motion of said second linear traverse.
 9. A micro-injection pump comprising: a syringe for supplying a fluid, said syringe having a plunger; a catheter arranged downstream of said syringe and in fluid communication therewith; a linear traverse operatively connected to said plunger for controllably discharging said fluid from said syringe; and computer control means connected to said linear traverse for controlling the motion of said linear traverse in accordance with a predetermined flow profile to discharge said fluid from said syringe at varying flow rates during a stroke of said plunger.
 10. The micro-injection pump according to claim 8, wherein said predetermined motion profile is selected by a user interfacing with said computer control means.
 11. The micro-injection pump according to claim 8, further comprising a flowmeter connected to said computer control means and arranged to measure flow from said syringe, wherein said computer control means includes a proportional plus integral plus derivative (P.I.D.) feedback control loop to ensure said predetermined flow profile is actually followed.
 12. A method of injecting a chosen fluid into the vasculature of a patient comprising the steps of: providing a first syringe and charging said first syringe with a conveying fluid; providing a second syringe and charging said second syringe with said chosen fluid, said second syringe communicating with an injection needle; enclosing a discharge tip of said injection needle within a fluid conduit in communication with said first syringe to establish a flow field of said conveying fluid surrounding said discharge tip; actuating said first and second syringes in a controlled manner to cause discrete boluses of said chosen fluid to be separated from said discharge tip of said injection needle with the aid of said flow field; providing a catheter in communication with said fluid conduit for carrying said boluses and said conveying fluid into said vasculature.
 13. The method according to claim 12, wherein said first and second syringes are actuated such that said boluses are separated from said discharge tip at a regular frequency.
 14. The method according to claim 12, wherein said chosen fluid is an insoluble contrast medium.
 15. The method according to claim 12, wherein said chosen fluid is a therapeutic fluid. 